In photographic industry there exists an ever lasting demand for photosensitive image-forming materials with increased sensitivity and image-quality. However both characteristics are often related which means that influencing one parameter will have its consequences for the other parameter and vice versa. This relationship can be clearly experienced in silver halide photographic materials. An increase of sensitivity of a photographic silver halide material can be realised by an increase of the mean size of the silver halide emulsion crystals of the said material. This action however results normally in a decrease of image quality. One way to solve this problem is to increase the efficiency of the electron-trapping of the latent-image in the silver halide grains. This can be realised by chemical sensitization in the presence of a chemical compound which can enhance the electron-trapping efficiency as mentioned herinbefore. This compound can be for instance a sulphur salt, a gold salt or a combination of both. In recent years chemical sensitization in the presence of a labile selenium compound is increasingly used. Examples of compounds which were suggested for use in order to get an increased sensitivity were substituted selenourea (as described e.g. in EP-A 0 280 031, EP-A 0 458 278), selenoethers (e.g. in JP-A 2-132434, JP-A 4-271341, JP-A 6-175258, U.S. Pat. No. 5,532,120), diselenides (e.g. in EP-A 0 703 492), selenoesters (e.g. in U.S. Pat. No. 5,306,613), selenoketones (e.g. in EP-A 0 476 345), phosphineselenides (e.g. in EP-A 0 506 009) and various others. However selenium sensitization easily causes fog as a result of the depth of the electron trap of the formed sensitivity speck which is larger than the depth of the sensitivity speck created by sulphur sensitization. At the same time the stability and the gradation of a selenium sensitized emulsion decrease if no precautions are taken. Special progress was announced by Yagihara M. in EP-A 0 585 787, describing chemical sensitization with seleno- or other chalcogenic compounds like R.sub.1 CO--Se--X--COR.sub.2 or (R.sub.3 CO--Se).sub.n MP, where R.sub.1, R.sub.2, R.sub.3 equals alkyl, aryl or heterocycle; X equals S, Se or Te; P equals a tri-alkyl- or tri-arylphosphonide; M equals a metal and n equals 1 or 2. Most of the patents dedicated to selenium sensitization like the ones mentioned hereinbefore are directed to the prevention of the described disadvantages. Additionally it is further known that sulphur or selenium sensitization carried out in the presence of a gold salt causes an increase in sensitivity but at the same time enhancing fog formation too. Particulary in comparison with gold-sulphur sensitization gold-selenium sensitization causes a remarkable rise in fog. However up to now the mechanism causing most of these effects is still not fully understood and a lot of work has to be done in order to get fundamental improvements in the prevention of fogging. Accordingly there has been a strong demand for selenium compounds which can give a substantial sensitivity increase while controlling fog to an acceptable low level. Such chemical selenium sensitizers give rise to silver halide emulsions with improved sensitivity-fog relationship. All the patents mentioned hereinbefore are more or less failing in disclosing a method for realizing high sensitive silver halide emulsions with low fog level by using the therein described selenium compounds.